1. Field of the Invention
The present invention relates to an active matrix liquid crystal display apparatus, and more particularly, to an opposed active matrix liquid crystal display apparatus having thin film transistors (TFTs) and liquid crystal cells, the TFTs corresponding to pixels, respectively, and being switched ON and OFF to write and hold voltages in the liquid crystal cells.
2. Description of the Related Art
Recently, active matrix liquid crystal display apparatuses have been widely used for lap-top personal computers, word processors, portable television sets, and the like, since the active matrix liquid crystal display apparatuses are thin similar to simple matrix liquid crystal display apparatuses. Note, pixels of the active matrix liquid crystal display apparatus are driven by the thin film transistors, respectively. Therefore, the display capacity and the number of lines of the display apparatus can be increased without deteriorating the drive duty, contrast, and angle of visibility, unlike the simple matrix liquid crystal display apparatus. The active matrix liquid crystal display apparatus realizes substantially the same color display quality as a cathode ray tube (CRT), and therefore, is useful as a flat display apparatus.
Since the active matrix liquid crystal display apparatus employs thin film transistors each serving as a switching element for each pixel, it inevitably involves complicated production processes. Large facilities will be required, therefore, to manufacture large-sized display apparatuses. In this way, the active matrix liquid display apparatuses involve expensive facilities and a poor yield, thereby increasing costs. Presently marketed active matrix liquid crystal display apparatuses are limited, therefore, to those of relatively small size.
In order to improve the yield of the active matrix liquid crystal display apparatuses, which is usually low because of their complicated structure, there has been proposed an opposed active matrix liquid crystal display apparatus involving scan bus lines and data bus lines formed on respective, different substrates so that the bus lines may not intersect one another. Improvement of display quality is also required.
A conventional active matrix liquid crystal display apparatus employs a single substrate on which scan bus lines and data bus lines are orthogonally formed, and display electrodes are connected to the intersections of the bus lines through thin film transistors. The scan bus lines and data bus lines intersect one another on the same substrate, and the conventional active matrix liquid crystal display apparatus sometimes has poor insulation causing short circuits at the intersections, or disconnections in upper bus lines owing to steps formed at the intersections. Since lower bus lines and an insulation layer cannot be unlimitedly thickened, it is not easy to reduce the resistance of the lower bus lines. When the insulation layer cannot be thickened, it is impossible to completely prevent short circuits at the intersections.
In order to solve the above problems, the opposed active matrix liquid crystal display apparatus has been proposed. In this display apparatus, scan bus lines and data bus lines are disposed on respective, different substrates such as glass substrates that face each other with a liquid crystal layer between them.
Note, in the opposed active matrix liquid crystal display apparatus, the data bus lines and scan bus lines are orthogonal to each other with the liquid crystal layer interposed between them, and thus it is not necessary to prepare an insulation layer for the intersections, thereby simplifying the structure. Further, the data bus lines and scan bus lines will not be short-circuited. This reduces display failure and improves an yield compared with the conventional, or normal-type, active matrix liquid crystal display apparatus.
Nevertheless, the opposed active matrix liquid crystal display apparatus frequently causes cross talk, and a liquid crystal cell voltage fluctuates owing to data voltages applied to the other cells, thereby to deteriorate display quality. In order to reduce the cross talk, compensate for the DC voltage level shift, and improve display quality, the inventors have proposed an active matrix liquid crystal display apparatus (Japanese Unexamined Patent Publication Ser. No. 4-102825 corresponding to U.S. patent application Ser. No. 07/695,029).